What’s the benefit to using EFS-Web?

EFS-Web offers you the ability to file patent applications and other patent documents electronically in a fraction of the time and at substantially less cost than paper filings. You forgo printing, postage, courier costs, and you receive immediate notification that your submission has been received. Unlike paper filings, most new applications submitted electronically can be viewed in Private PAIR within an hour after filing.

USPTO FAQ - Questions and Answers (08JUL2007)